It is well known that phenolic compounds are effective in stabilizing polymer compositions against the degradation caused by exposure to heat, oxygen and shear forces experienced during melt processing. However, it is also known that the use of phenolic stabilizers tends to be accompanied by discoloration of the polymer composition and so polymer stabilization generally involves the use of a combination of additives designed to achieve a combination of stabilization and color retention.
For example, U.S. Pat. No. 4,590,231 discloses a stabilized polyolefin composition containing a phenolic antioxidant and an ultraviolet light absorber which is stabilized against discoloration upon exposure to heating, to the combustion products of natural gas or to storage for prolonged periods at ambient temperatures by the presence of a hydroxylamine derivative of the formula T1N(OH)T2 where T1 is alkyl of 1 to 36 carbon atoms, cycloalkyl of 5 to 12 carbon atoms, aralkyl of 7 to 9 carbon atoms, or said aralkyl substituted by alkyl of 1 to 4 carbon atoms or by one or two halogen atoms, T2 is hydrogen, or independently has the same meaning as T1; and the carbon content of T1 and T2 together is 6 to 36 carbon atoms. Preferred phenolic antioxidants include neopentanetetrayl tetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), n-octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate, 2,6-di-tert-butyl-p-cresol and 2,2′-ethylidene-bis(4,6-di-tert-butylphenol).
A similar stabilized polyolefin composition containing a phenolic antioxidant combined with a long chain N,N-dialkylhydroxyamine is disclosed in U.S. Pat. No. 4,876,300. Preferred phenolic antioxidants include n-octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, neopentanetetrayl tetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), di-noctadecyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, thiodiethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 3,6-dioxaoctamethylene bis(3-methyl-5-tert-butyl-4-hydroxyhydrocinnamate), 2,6-di-tert-butyl-p-cresol, 2,2′-ethylidene-bis(4,6-di-tert-butylphenol), 1,3,5-tris(2,6-dimethyl-4-tert-butyl-3-hydroxybenzyl)iso-cyanurate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,3,5-tris[2-(3,5-di-tertbutyl4-hydroxyhydrocinnamoyloxy)-ethyl]isocyanurate, 3,5-di-(3,5-di-tert-butyl-4-hydroxybenzyl)mesitol, hexamethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), 1-(3,5-di-tert-butyl-4-hydroxyanilino)-3,5-di(octylthio)-s-triazine, N,N′-hexamethylene-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide), calcium bis(O-ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate), ethylene bis[3,3-di(3-tert-butyl-4-hydroxyphenyl)butyrate], octyl 3,5-di-tert-butyl-4-hydroxybenzylmercaptoacetate, bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazide, and N,N′-bis[2(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy)-ethyl]oxamide and 3,6-dioxaoctamethylene bis(3,5-di-tert-butyl-4hydroxyhydrocinnamate).
U.S. Pat. No. 5,844,029 discloses a method for improving the yellowness index and melt stability of a thermoplastic resin by admixing therewith a saturated hydrocarbon amine oxide and a second stabilizer. The amine oxide has the formula R1R2R3N→O, wherein R1, R2 and R3 are independently selected from alkyl, aryl, aralkyl, alkaryl, cycloalkyl, alkcycloalkyl and cycloalkalkyl and each have from 1 to 36 carbon atoms per group, provided that if one R1, R2 and R3 is an alkyl group having from 6 to 36 carbon atoms per group, then the other two of R1, R2 and R3 cannot both be alkyl groups having from 1 to 5 carbon atoms per group. The second stabilizer is selected from selected from phenolic antioxidants, hindered amine light stabilizers, ultraviolet light absorbers, organic phosphorus compounds, alkaline metal salts of fatty acids, and thiosynergists.
U.S. Pat. No. 5,922,794 discloses a stabilized thermoplastic resin composition includes a stabilizing amount of (a) a stabilizer selected from the group consisting of the phenolic antioxidants, the 3-arylbenzofuranones, the hindered amine stabilizers, the ultraviolet light absorbers, the organic phosphorus compounds, the alkaline metal salts of fatty acids, the hydroxylamines, and the thiosynergists, and (b) a stabilizing amount of a tertiary amine oxide selected from the group consisting of dioctyl methyl amine oxide, trioctyl amine oxide, didecyl methyl amine oxide, tridecyl amine oxide, di(coco alkyl) methyl amine oxide, tri(coco alkyl) amine oxide, di(tallow alkyl) methyl amine oxide, tri(tallow alkyl) amine oxide, tri(C20-C22) amine oxide, di(C20-C22 alkyl) methyl amine oxide, and mixtures thereof. Preferred phenolic antioxidants include n-octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, neopentanetetrayl tetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), di-n-octadecyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate, thiodiethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), 1,3,5-methyl-2,4-6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 3,6-di-oxaoctamethylene bis(3-methyl-5-tert-butyl-4-hydroxyhydrocinnamate), 2,6-di-tert-butyl-p-cresol, 2,2′-ethylidene-bis(4,6-di-tert-butylphenol), 1,3,5-tris(2,6-dimethyl4-tert-butyl-3-hydroxybenzyl)isocyanurate, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,3,5-tris[2-(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy)-ethyl]-isocyanurate, 3,5-di-(3,5-di-tert-butyl-4-hydroxybenzyl)-mesitol, hexamethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), 1-(3,5-di-tert-butyl-4-hydroxyanilino)-3,-5-di(octylthio)-s-triazine, N,N′-hexamethylene-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide), calcium bis(ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate), ethylene bis[3,3-di(3-tert-butyl-4-hydroxyphenyl)butyrate], octyl 3,5-di-tert-butyl-4-hydroxybenzylmercaptoacetate, bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazide, and N,N′-bis[2-(3,5di-tert-butyl-4-hydroxyhydroxocinnamoyloxy)ethyl]oxamide.
US Published Patent Application No 2006/0089437 discloses a liquid stabilizing mixture for organic polymers or copolymers comprising: (a) a liquid compound selected from the group consisting of esters or mixtures of esters of sterically hindered phenols having the formula
wherein R1 and R2, the same or different, are a linear or branched C1-C18 alkyl group and R3 is a linear or branched C8-C18 alkyl group, and (b) solid compound selected from the group consisting of sterically hindered phenols having the formula:
wherein n is an integer ranging from 0 to 10 and wherein the mixture is permanently liquid both at room temperature and temperatures as low as −30° C. The liquid stabilizing mixture can also include a wide variety of co-stabilizers such as phosphites; such as tris(2,4-di-t-butylphenyl) phosphite; hydroxylamines, such as N,N-dihexadecylhydroxylamine and N,N-dioctadecylhydroxylamine; and nitrons, such as N-tetradecyl-α-tridecyl-nitron, N-hexadecyl-α-pentadecyl-nitron, and N-octadecyl-α-heptadecyl-nitron.
The solid sterically hindered phenol disclosed in US Published Patent Application No 2006/0089437 is the reaction product of p-cresol, dicyclopentadiene and isobutylene and is commercially available under the tradename Lowinox® CPL. Lowinox® CPL is known as a polymer antioxidant with low discoloring properties. However, according to the present invention, it has now been found combining Lowinox® CPL with a tertiary amine oxide can produce a polymer stabilizing composition with an unexpected and highly advantageous combination of color retention and antioxidant properties.